To investigate the association between postoperative CA-125 levels and overall survival (OS) in patients with ovarian cancer, assessing its potential role as a prognostic biomarker. Observational study. Place and Duration of the Study: Department of Medical Oncology, Faculty of Medicine, Celal Bayar University, Manisa, Turkiye, from February 2012 to November 2024. The medical records of 211 women diagnosed with ovarian cancer were retrospectively reviewed. Descriptive statistical analyses were conducted to investigate the relationship between CA-125 levels and OS. Patients were categorised into high and low perioperative CA-125 groups based on predefined cut-off values: 305 U/mL preoperatively and 30.4 U/mL postoperatively. The predictive performance of preoperative and postoperative CA-125 levels for ovarian cancer recurrence was assessed using receiver operating characteristic (ROC) analysis. The Kaplan-Meier survival curves were employed to estimate OS, and the Cox regression analysis was performed for univariate and multivariate assessments. Significant differences in OS were observed between the patients with low versus high postoperative CA-125 levels: 1-year OS (93.3% vs. 81.8%), 3-year OS (87.8% vs. 48.1%), 5-year OS (73.3% vs. 35.4%), and 10-year OS (52.0% vs. 19.7%) (p <0.001). Furthermore, postoperative CA-125 levels were independent predictors of both OS (univariate: p <0.001; multivariate: p = 0.009) and progression-free survival (PFS) (univariate: p = 0.005; multivariate: p = 0.011). Perioperative CA-125 levels hold significant prognostic value in ovarian cancer management, offering a valuable biomarker for predicting survival outcomes and disease progression. Postoperative CA-125, Tumour marker, Ovarian cancer, Overall survival, Prognostic marker.